Galanin receptors: involvement in feeding, pain, depression and Alzheimer's disease

Co-aggregation and secondary nucleation in the life cycle of human prolactin/galanin functional amyloids

Synergistic-aggregation and cross-seeding by two different proteins/peptides in the amyloid aggregation are well evident in various neurological disorders including Alzheimer’s disease. Here, we show co-storage of human Prolactin (PRL), which is associated with lactation in mammals, and neuropeptide galanin (GAL) as functional amyloids in secretory granules (SGs) of the female rat. Using a wide variety of biophysical studies, we show that irrespective of the difference in sequence and structure, both hormones facilitate their synergic aggregation to amyloid fibrils. Although each hormone possesses homotypic seeding ability, a unidirectional cross-seeding of GAL aggregation by PRL seeds and the inability of cross seeding by mixed fibrils suggest tight regulation of functional amyloid formation by these hormones for their efficient storage in SGs. Further, the faster release of functional hormones from mixed fibrils compared to the corresponding individual amyloid, suggests a novel mechanism of heterologous amyloid formation in functional amyloids of SGs in the pituitary.

The formation of plaques of proteins called ‘amyloids’ in the brain is one of the hallmark characteristics of both Alzheimer’s and Parkinson’s disease, but amyloids can form in many tissues and organs, often disrupting normal activity. A lot of the research into amyloids has focused on their role in disease, but it turns out that amyloids can also appear in healthy tissues. For example, some protein hormones form amyloids that act as storage depots, helping cells to release the hormone when it is needed.

Normally, amyloids are made mostly of a single type of protein or protein fragment associated with a particular disease like Alzheimer's. Often, this type of amyloid promotes plaque formation in other proteins, which aggravates other diseases (for example, the amyloids that form in Alzheimer’s can lead to Parkinson’s disease or type II diabetes getting worse).The plaques start growing from small amyloid fragments called seeds. In mixed amyloids – amyloids made of two types of proteins – seeds made of one protein can trigger the formation of amyloids of the other protein. This raises the question, is this true for hormones? The body often releases more than one hormone at a time from the same tissue; for example, the pituitary gland releases prolactin and galanin simultaneously. However, these hormones have completely different structures, so whether they can form a mixed amyloid is unclear.

To answer this question, Chatterjee et al. first determined that, within the pituitary gland of female rats, prolactin and galanin could be found together in the same cells, forming mixed amyloids. To understand out how this happens, Chatterjee et al. tried seeding new amyloids using either prolactin or galanin. This revealed that only prolactin seeds were able to trigger the formation of galanin amyloids. Chatterjee et al. also found that the mixed amyloids could release the hormones faster than amyloids made from either protein alone. Together, these results suggest that the collaboration between these two proteins may help maintain hormone balance in the body.

Problems with hormone storage and release lead to various human diseases, including prolactinoma. Understanding amyloid storage depots could reveal new ways to control hormone levels. Further research could also help to explain more about well-studied diseases linked to amyloids, like Alzheimer's.

Activation of Galanin Receptor 1 with M617 Attenuates Neuronal Apoptosis via ERK/GSK-3β/TIP60 Pathway After Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Neuronal apoptosis plays an important pathological role in early brain injury after SAH. Galanin receptor 1 (GalR1) activation was recently shown to be anti-apoptotic in the setting of ischemic stroke. This study aimed to explore the anti-neuronal apoptosis effect of GalR1 activation after SAH, as well as the underlying mechanisms. GalR1 CRISPR and GalR1 selective agonist, M617, was administered, respectively. Extracellular-signal-regulated kinase (ERK) inhibitor (U0126) and glycogen synthase kinase 3-beta (GSK3-β) CRISPR were administered to investigate the involvement of the ERK/GSK3-β pathway in GalR1-mediated neuroprotection after SAH. Outcome assessments included neurobehavioral tests, western blot, and immunohistochemistry. The results showed that endogenous ligand galanin (Gal) and GalR1 were markedly increased in the ipsilateral brain hemisphere at 12 h and 24 h after SAH. GalR1 were expressed mainly in neurons, but expression was also observed in some astrocytes and microglia. GalR1 CRISPR knockdown exacerbated neurological deficits and neuronal apoptosis 24 h after SAH. Moreover, activation of GalR1 with M617 significantly improved short- and long-term neurological deficits but decreased neuronal apoptosis after SAH. Furthermore, GalR1 activation dysregulated the protein levels of phosphorylated ERK and GSK-3β, but downregulated the phosphorylated Tat-interactive protein 60 (TIP60) and cleaved caspase-3 at 24 h after SAH. GalR1 CRISPR, U0126, and GSK-3β CRISPR abolished the beneficial effects of GalR1 activation at 24 h after SAH in rats. Collectively, the present study demonstrated that activation of GalR1 using M617 attenuated neuronal apoptosis through the ERK/GSK-3β/TIP60 pathway after SAH in rats. GalR1 may serve as a promising therapeutic target for SAH patients.

Beneficial effects of galanin system on diabetic peripheral neuropathic pain and its complications

Diabetic peripheral neuropathic pain (DPNP) is a distal spontaneous pain, caused by lesion of sensory neurons and accompanied by depression and anxiety frequently, which reduce life quality of patients and increase society expenditure. To date, antidepressants, serotonin-noradrenaline reuptake inhibitors and anticonvulsants are addressed as first-line therapy to DPNP, alone or jointly. It is urgently necessary to develop novel agents to treat DPNP and its complications. Evidences indicate that neuropeptide galanin can regulate multiple physiologic and pathophysiological processes. Pain, depression and anxiety may upregulate galanin expression. In return, galanin can modulate depression, anxiety, pain threshold and pain behaviors. This article provides a new insight into regulative effects of galanin and its subtype receptors on antidepressant, antianxiety and against DPNP. Through activating GALR1, galanin reinforces depression-like and anxiogenic-like behaviors, but exerts antinociceptive roles. While via activating GALR2, galanin is referred to as anti-depressive and anti-anxiotropic compounds, and at low and high concentration facilitates and inhibits nociceptor activity, respectively. The mechanism of the galanin roles is relative to increase in K⁺ currents and decrease in Ca²⁺ currents, as well as neurotrophic and neuroprotective roles. These data are helpful to develop novel drugs to treat DPNP and its complications.

A preliminary study on DRGs and spinal cord of a galanin receptor 2-EGFP transgenic mouse

The neuropeptide galanin functions via three G-protein coupled receptors, Gal_1-3-R. Both Gal₁-R and ₂-R are involved in pain signaling at the spinal level. Here a Gal₂-R-EGFP transgenic (TG) mouse was generated and studied in pain tests and by characterizing Gal₂-R expression in both sensory ganglia and spinal cord. After peripheral spared nerve injury, mechanical allodynia developed and was ipsilaterally similar between wild type (WT) and TG mice. A Gal₂-R-EGFP-positive signal was primarily observed in small and medium-sized dorsal root ganglion (DRG) neurons and in spinal interneurons and processes. No significant difference in size distribution of DRG neuronal profiles was found between TG and WT mice. Both percentage and fluorescence intensity of Gal₂-R-EGFP-positive neuronal profiles were overall significantly upregulated in ipsilateral DRGs as compared to contralateral DRGs. There was an ipsilateral reduction in substance P-positive and calcitonin gene-related peptide (CGRP)-positive neuronal profiles, and this reduction was more pronounced in TG as compared to WT mice. Moreover, Gal₂-R-EGFP partly co-localized with three pain-related neuropeptides, CGRP, neuropeptide Y and galanin, both in intact and injured DRGs, and with galanin also in local neurons in the superficial dorsal horn. Taken together, the present results provide novel information on the localization and phenotype of DRG and spinal neurons expressing the second galanin receptor, Gal₂-R, and on phenotypic changes following peripheral nerve injury. Gal2-R may also be involved in autoreceptor signaling.

NALCN channels enhance the intrinsic excitability of spinal projection neurons

Spinal projection neurons convey nociceptive signals to multiple brain regions including the parabrachial (PB) nucleus, which contributes to the emotional valence of pain perception. Despite the clear importance of projection neurons to pain processing, our understanding of the factors that shape their intrinsic membrane excitability remains limited. Here, we investigate a potential role for the Na leak channel NALCN in regulating the activity of spino-PB neurons in the developing rodent. Pharmacological reduction of NALCN current (INALCN), or the genetic deletion of NALCN channels, significantly reduced the intrinsic excitability of lamina I spino-PB neurons. In addition, substance P (SP) activated INALCN in ascending projection neurons through downstream Src kinase signaling, and the knockout of NALCN prevented SP-evoked action potential discharge in this neuronal population. These results identify, for the first time, NALCN as a strong regulator of neuronal activity within central pain circuits and also elucidate an additional ionic mechanism by which SP can modulate spinal nociceptive processing. Collectively, these findings indicate that the level of NALCN conductance within spino-PB neurons tightly governs ascending nociceptive transmission to the brain and thereby potentially influences pain perception.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Modification of Anxious Behavior after Psychogenic Trauma and Treatment with Galanin Receptor Antagonist

Effects of blockage of central galanin receptors on anxiety manifestations were studied in rats with psychogenic trauma. Psychogenic trauma was modeled by exposure of a group of rats to the situation when the partner was killed by a predator. Antagonist of galanin receptors was intranasally administered before stress exposure. Animal behavior was evaluated using the elevated-plus maze test, free exploratory paradigm, and open-field test. Psychogenic trauma was followed by an increase in anxiety level and appearance of agitated behavior. Blockage of galanin receptors aggravated behavioral impairment, which manifested in the pathological anxious reactions - manifestations of hypervigilance and hyperawareness. The results suggest that endogenous pool of galanin is involved into prevention of excessive CNS response to stressful stimuli typical of posttraumatic stress disorder.

Regulation of glucose and insulin release following acute and repeated treatment with the synthetic galanin analog NAX-5055

The neuropeptide galanin is widely expressed in both the central and peripheral nervous systems. However there is limited understanding of how individual galanin receptor (GalR1, 2, and 3) subtypes mediate the physiological activity of galanin in vivo. To address this issue we utilized NAX-5055, a systemically available, metabolically stable galanin analog. NAX-5055 displays a preference for GalR1 receptors and possesses potent anticonvulsant activity in vivo, suggesting that NAX-5055 engages central galanin receptors. To determine if NAX-5055 also modulates the activity of peripheral galanin receptors, we evaluated the effect of NAX-5055 on blood glucose and insulin levels in mice. Acute and repeated (once daily for four days) systemic administration of NAX-5055 (4 mg/kg) significantly increased blood glucose levels compared to vehicle treated mice. However, a hyperglycemic response was not observed following systemic administration of NAX-805-1, a scrambled analog of NAX-5055, with critical receptor binding residues, Trp(2) and Tyr(9), reversed. These results suggest that chemical modifications independent of the galanin backbone of NAX-5055 are not responsible for the hyperglycemic response. The effect of NAX-5055 on glucose homeostasis was further evaluated with a glucose tolerance test (GTT). Mice administered either acute or repeated (once daily for four days) injections of NAX-5055 (4 mg/kg) displayed impaired glucose handling and reduced insulin response to an acute glucose (1g/kg) challenge. Here we have shown that systemic administration of a centrally active GalR1-preferring galanin analog produces acute hyperglycemia and an inhibition of insulin release in vivo and that these effects are not attenuated with repeated administration. NAX-5055 thus provides a new pharmacological tool to further the understanding of function of both central and peripheral GalR1 receptors in vivo.

Differential effects of prenatal stress in female 5-HTT-deficient mice: towards molecular mechanisms of resilience

Prenatal stress (PS) exposure is known to increase the risk of developing emotional disorders like major depression in later life. However, some individuals do not succumb to adversity following developmental stress exposure, a phenomenon referred to as resilience. To date, the molecular mechanisms explaining why some subjects are vulnerable and others more resilient to PS are far from understood. Recently, we have shown that the serotonin transporter (5-HTT) gene may play a modulating role in rendering individuals susceptible or resilient to PS. However, it is not clear which molecular players are mediating the interaction between PS and the 5-Htt genotype in the context of vulnerability and resilience to PS. For this purpose, we performed a microarray study with the help of Affymetrix GeneChip® Mouse Genome 430 2.0 Array, in which we separated wild-type and heterozygous 5-Htt-deficient (5-Htt+/-) PS offspring into susceptible and resilient offspring according to their performance in the forced swim test. Performance-oriented LIMMA analysis on the mRNA expression microarray data was followed by subsequent Spearman's correlation analysis linking the individual qRT-PCR mRNA expression data to various anxiety- and depression-related behavioral and neuroendocrine measures. Results indicate that, amongst others, Fos-induced growth factor (Figf), galanin receptor 3 (Galr3), growth hormone (Gh) and prolactin (Prl) were differentially expressed specifically in resilient offspring when compared to controls, and that the hippocampal expression of these genes showed several strong correlations with various measures of the hypothalamus-pituitary-adrenal axis (re)activity. In conclusion, there seems to be an intricate interplay between the expression of Figf, Galr3, Gh and Prl and neuroendocrine regulation, which may be critical in mediating resilience to PS exposure. More insight into the exact role of these molecular players may significantly enhance the development of new treatment strategies for stress-related emotional disorders.

The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats

BACKGROUND/OBJECTIVE

The galanin-3 receptor (GALR3) subtype has been identified as having a role in both feeding behaviour and the regulation of emotional states including anxiety. Despite the evidence for an association between galanin and alcohol, the current study is the first to explore the direct role of GALR3 in this context. The present study investigated the potential of the novel selective GALR3 antagonist, SNAP 37889, to reduce anxiety-like behaviour and voluntary ethanol consumption in the iP (alcohol-preferring) rat. This was achieved through a number of behavioural paradigms testing for anxiety, along with the operant self-administration model.

RESULTS

Overall, male iP rats treated with SNAP 37889 at a dose of 30 mg/kg (i.p.) did not show altered locomotor activity or changes in anxiety-like behaviour in the elevated plus maze or light-dark paradigms. Treatment with SNAP 37889 (30 mg/kg, i.p.) reduced operant responding for solutions containing ethanol, sucrose and saccharin. Collectively, results from the current study showed that SNAP 37889 (30 mg/kg, i.p.) is effective in reducing operant responding for ethanol, independent of a sedative effect.

CONCLUSIONS

These findings provide evidence that GALR3 antagonism reduces alcohol consumption and further suggest that GALR3 may be implicated in the rewarding effects of natural and drug reinforcers.

Behavioral effects of neuropeptides in rodent models of depression and anxiety

In recent years, studies have advocated neuropeptide systems as modulators for the behavioral states found in mood disorders such as depression and anxiety disorders. Neuropeptides have been tested in traditional animal models and screening procedures that have been validated by known antidepressants and anxiolytics. However, it has become clear that although these tests are very useful, neuropeptides have distinct behavioral effects and dose-dependent characteristics, and therefore, use of these tests with neuropeptides must be done with an understanding of their unique characteristics. This review will focus on the behavioral actions of neuropeptides and their synthetic analogs, particularly in studies utilizing various preclinical tests of depression and anxiety. Specifically, the following neuropeptide systems will be reviewed: corticotropin-releasing factor (CRF), urocortin (Ucn), teneurin C-terminal associated peptide (TCAP), neuropeptide Y (NPY), arginine vasopressin (AVP), oxytocin, the Tyr-MIF-1 family, cholecystokinin (CCK), galanin, and substance P. These neuropeptide systems each have a unique role in the regulation of stress-like behavior, and therefore provide intriguing therapeutic targets for mood disorder treatment.

Neuropeptide and sigma receptors as novel therapeutic targets for the pharmacotherapy of depression

Among the most prevalent of mental illnesses, depression is increasing in incidence in the Western world. It presents with a wide variety of symptoms that involve both the CNS and the periphery. Multiple pharmacological observations led to the development of the monoamine theory as a biological basis for depression, according to which diminished neurotransmission within the CNS, including that of the dopamine, noradrenaline (norepinephrine) and serotonin systems, is the leading cause of the disorder. Current conventional pharmacological antidepressant therapies, using selective monoamine reuptake inhibitors, tricyclic antidepressants and monoamine oxidase inhibitors, aim to enhance monoaminergic neurotransmission. However, the use of these agents presents severe disadvantages, including a delay in the alleviation of depressive symptoms, significant adverse effects and high frequencies of non-responding patients. Neuroendocrinological data of recent decades reveal that depression and anxiety disorders may occur simultaneously due to hypothalamus-pituitary-adrenal (HPA) axis hyperactivity. As a result, the stress-diathesis model was developed, which attempts to associate genetic and environmental influences in the aetiology of depression. The amygdala and the hippocampus control the activity of the HPA axis in a counter-balancing way, and a plethora of regulatory neuropeptide signalling pathways are involved. Intervention at these molecular targets may lead to alternative antidepressant therapeutic solutions that are expected to overcome the limitations of existing antidepressants. This prospect is based on preclinical evidence from pharmacological and genetic modifications of the action of neuropeptides such as corticotropin-releasing factor, substance P, galanin, vasopressin and neuropeptide Y. The recent synthesis of orally potent non-peptide micromolecules that can selectively bind to various neuropeptide receptors permits the onset of clinical trials to evaluate their efficacy against depression.

Selective stimulation of GalR1 and GalR2 in rat substantia gelatinosa reveals a cellular basis for the anti- and pro-nociceptive actions of galanin

Galanin modulates spinal nociceptive processing by interacting with two receptors, GalR1 and GalR2. The underlying neurophysiological mechanisms were examined by whole-cell recording from identified neurons in the substantia gelatinosa of young adult rats. GalR1 was activated with a 'cocktail' containing the GalR1/2 agonist, AR-M 961 (0.5 microM), in the presence of the GalR2 antagonist, M871 (1.0-2.5 microM). GalR2 was activated with the selective agonist, AR-M 1896 (0.5-1.0 microM). Application of the 'GalR1 agonist cocktail' often activated an inwardly-rectifying conductance in delay firing (excitatory) and tonically firing (inhibitory) neurons. This conductance was not activated by AR-M 1896 which instead decreased or increased an outwardly-rectifying conductance at voltages positive to -70 mV. Despite this variability in its actions on current-voltage relationships, AR-M 1896 very consistently decreased membrane excitability, as measured by cumulative action potential latency in response to a depolarizing current ramp. This strong GalR2-mediated effect was seen in neurons where membrane conductance was decreased, and where membrane excitability might be predicted to increase. GalR2 was also located presynaptically, as AR-M 1896 increased the interevent interval of spontaneous EPSCs in both delay and tonic cells. By contrast, the 'GalR1 agonist cocktail' had little effect on spontaneous EPSCs, suggesting that presynaptic terminals do not express GalR1. These diverse actions of GalR1 and GalR2 activation on both inhibitory and excitatory neurons are discussed in relation to the known spinal antinociceptive and pro-nociceptive actions of galanin, to the possible association of GalR1 with the inhibitory G-protein, G(i/o) and to report that GalR2 activation suppresses Ca2+ channel currents.

Involvement of galanin receptors 1 and 2 in the modulation of mouse vagal afferent mechanosensitivity

It is established that the gut peptide galanin reduces neuronal excitability via galanin receptor subtypes GALR1 and GALR3 and increases excitability via subtype GALR2. We have previously shown that galanin potently reduces mechanosensitivity in the majority of gastro-oesophageal vagal afferents, and potentiates sensitivity in a minority. These actions may have implications for therapeutic inhibition of gut afferent signalling. Here we investigated which galanin receptors are likely to mediate these effects. We performed quantitative RT-PCR on RNA from vagal (nodose) sensory ganglia, which indicated that all three GALR subtypes were expressed at similar levels. The responses of mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated before and during application of galanin receptor ligands to their peripheral endings. Two types of vagal afferents were tested: tension receptors, which respond to circumferential tension, and mucosal receptors which respond only to mucosal stroking. Galanin induced potent inhibition of mechanosensitivity in both types of afferents. This effect was totally lost in mice with targeted deletion of Galr1. The GALR1/2 agonist AR-M961 caused inhibition of mechanosensitivity in Galr1+/+ mice, but this was reversed to potentiation in Galr1-/- mice, indicating a minor role for GALR2 in potentiation of vagal afferents. We observed no functional evidence of GALR3 involvement, despite its expression in nodose ganglia. The current study highlights the complex actions of galanin at different receptor subtypes exhibiting parallels with the function of galanin in other systems.

Galanin expressed in the excitatory fibers attenuates synaptic strength and generalized seizures in the piriform cortex of mice

The neuropeptide galanin is considered to be an endogenous antiepileptic agent, presumably acting via inhibition of glutamate release. Previously, we have demonstrated that in mice ectopically overexpressing galanin in cortical and hippocampal neurons, particularly in granule cells and their axons, the mossy fibers, hippocampal kindling epileptogenesis is suppressed and is associated with attenuated frequency facilitation in mossy fiber-CA3 cell synapses. We hypothesized that changes in synaptic transmission might occur also in other excitatory synapses of the galanin overexpressing (GalOE) mouse, contributing to seizure suppression. Lateral olfactory tract (LOT) synapses, formed by axons of olfactory bulb (OB) mitral cells and targeting piriform cortex (PC) pyramidal cells, ectopically express galanin in GalOE mice. Using whole-cell patch-clamp recordings, we found that excitatory synaptic responses recorded in PC pyramidal cells during high frequency stimulation of the LOT were attenuated in GalOE mice as compared to wild-type controls. This effect was mimicked by bath application of galanin or its agonist galnon to wild-type slices, supporting the notion of ectopic galanin action. Since the high frequency activation induced in vitro resembles epileptic seizures in vivo, we asked whether the observed synaptic inhibition would result in altered epileptogenesis when animals were kindled via the same synapses. In male GalOE mice, we found that the latency to convulsions was prolonged, and once animals had experienced the first stage 5 seizure, generalized seizures were less sustainable. These data indicate that the PC is a possible target for epilepsy treatment by ectopically overexpressing galanin to modulate seizure activity.

Amino substituted analogs of 1-phenyl-3-phenylimino-2-indolones with potent galanin Gal3 receptor binding affinity and improved solubility

A series of amino analogs of 1,3-dihydro-1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one (1) were synthesized to improve aqueous solubility, while retaining high affinity for the human galanin Gal3 receptor. A very potent analog (9e, 1,3-dihydro-1-[3-(2-pyrrolidinylethoxy)phenyl]-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one, Ki=5 nM) shows good selectivity and solubility of 48 microg/mL at pH 7.4.

A novel, systemically active, selective galanin receptor type-3 ligand exhibits antidepressant-like activity in preclinical tests

The neuropeptide galanin is widely expressed in limbic nuclei in the brain, and plays an important role in the regulation of homeostatic and affective behaviors, in part through its modulation of central monoamine pathways. Recent evidence suggests that galanin and its receptors may be involved in the efficacy of various modalities of antidepressant treatments. We have previously demonstrated that systemically active, non-peptide galanin receptor type-1/2 agonists exhibit antidepressant-like effects in the rat forced swim test. Here we evaluate a novel galanin receptor type-3 (GalR3) antagonist in preclinical tests of anxiety and depression. At multiple doses, the compound displayed no effects in the elevated plus maze in mice. By contrast, the compound decreased time spent immobile in the tail suspension test by mice. Additionally, the GalR3 drug decreased time spent immobile in the forced swim test in rats, similarly to the effects of desipramine, yet did not increase locomotor activity in an open field test. These combined data from two species indicate that GalR3 receptor antagonists may exhibit antidepressant-like effects.

Specific expression of galanin in the peri-infarct zone after permanent focal cerebral ischemia in the rat

Galanin (Gal) is a neuropeptide with supposed neurotrophic-like action. In the present study, expression of Gal has been investigated in the core and peri-infarct zone at 1, 4, 24 and 72 h after middle cerebral artery occlusion (MCAo) in the rat. Three days after MCAo a small but consistent number of morphological intact Gal-positive neuronal cells were observed in the peri-infarct zone. Gal-positive cells were barely detectable in the infarct and peri-infarct zone at 24 h. No Gal immunopositive cells were detected in brain subjected to 1 and 4 h of ischemia. Gal immunoreactivity was also detected in myelinated fibers 4 and 24 h after focal ischemia. Gal may be a peptide with neurotrophic and plasticity functions under stress conditions.

Role of galanin receptor 1 and galanin receptor 2 activation in synaptic plasticity associated with 3',5'-cyclic AMP response element-binding protein phosphorylation in the dentate gyrus: studies with a galanin receptor 2 agonist and galanin receptor 1 knockout mice

The neuropeptide galanin was shown to impair cognitive performance and reduce hippocampal CA1 long-term potentiation (LTP) in rodents. However, the contribution of the two main galanin receptors; GalR1 and GalR2, present in the hippocampus to these effects is not known. In the present study, we determined the protein expression levels of GalR1 and GalR2 in the mouse dentate gyrus (DG) and used galanin (2-11), a recently introduced GalR2 agonist, and GalR1 knockout mice to examine the contribution of GalR1 and GalR2 to the modulation of LTP and 3',5'-cyclic AMP response element-binding protein (CREB)-dependent signaling cascades. In the DG, 57+/-5% of the galanin binding sites were GalR2, and the remaining population corresponded to GalR1. In hippocampal slices, galanin (2-11) fully blocked the induction of DG LTP, whereas galanin (1-29), a high affinity agonist for both GalR1 and GalR2, strongly but not fully attenuated the late phase of LTP by 80+/-1.5%. Application of galanin (1-29) or galanin (2-11) after LTP induction caused a transient reduction in the maintenance phase of LTP, with the larger effect displayed by superfusion of galanin (2-11). The induction and maintenance of DG LTP was not altered in the GalR1 knockout mice. Superfusion of galanin (1-29) or galanin (2-11) blocked the LTP induction to the same degree indicating a role for GalR2 in the induction phase of DG LTP. Furthermore, we analyzed the effects of GalR1 and/or GalR2 activation on DG LTP-induced CREB phosphorylation, associated with the late transcriptional effects of LTP. In the lateral part of the granule cell layer, high-frequency trains stimulation caused a significant increase in the level of CREB phosphorylation, which was significantly reduced by application of either galanin (1-29) or galanin (2-11), indicating that both GalR1 and/or GalR2 can mediate some of their effects on LTP through inhibition of CREB-related signaling cascades.

Effect of galnon on induction of long-term potentiation in dentate gyrus of C57BL/6 mice

The impairment of cognitive performance by galanin administration in rodents indicates a possible modulating effect of this neuropeptide on long-term potentiation (LTP) induction in the hippocampal formation. Galnon is a non-peptide, systemically active galanin receptor agonist which has been tested in feeding, seizure and forced swim task in in vivo rodent experimental models. Similarly to galanin (1-29) (i.c.v.), galnon (i.p.) has exhibited anticonvulsant effects in rats. We have investigated the effect of galnon on the synaptic transmission and plasticity in hippocampal dentate gyrus (DG) of C57Bl/6 mice and compared the galnon effects to the effect of galanin (1-29) and galmic, a non-peptide galanin receptor agonist. Similarly to galanin (1-29) and galmic, superfusion of galnon did not alter the input-output responses in DG. Administration of galnon (1 microM) significantly attenuated the LTP induction by 85.5 +/- 1% by 51 min after high frequency trains stimulation. This result was very similar to the effect of galanin (1-29) and galmic, which caused an 80 +/- 1.5% and 94 +/- 2% reduction in the level of field potentiation, respectively. The PPF responses, however, were not altered due to galnon superfusion which is in contrast to the effect of galanin (1-29) or galmic. In summary, these data indicate that the systemically active, non-peptide galanin receptor agonist, galnon can exert similar effects to galanin (1-29) in attenuation of DG LTP in mice.

Neuronal interactions between galanin-like-peptide- and orexin- or melanin-concentrating hormone-containing neurons

Galanin-like peptide (GALP) is a novel orexigenic neuropeptide that is recently isolated from the porcine hypothalamus. GALP-containing neurons predominantly locate in the hypothalamic arcuate nucleus (ARC). The expression of GALP mRNA within the ARC is increased after the administration of leptin. GALP-containing neurons express leptin receptor and contain alpha-melanocyte-stimulating hormone. We have recently reported that neuropeptide Y (NPY)- and orexin-containing axon terminals are in close apposition with GALP-containing neurons in the ARC. In addition, GALP-containing neurons express orexin-1 receptor (OX1-R). Thus, GALP may function under the influence of leptin and orexin. However, the target neurons of GALP have not yet been clarified. To clarify the neuronal interaction between GALP-containing and other feeding regulating neurons, double-immunostaining method using antibodies against GALP- and orexin- or melanin-concentrating hormone (MCH) was performed in the rat lateral hypothalamus (LH). GALP-immunoreactive fibers appeared to project to the LH around the fornix. They were also found from the rostral to the caudal part of the ARC, paraventricular nucleus (PVH), stria terminalis (BST), medial preoptic area (MPA), and lateral septal nucleus (LSV). Moreover, GALP-like immunoreactive nerve fibers were directly contacted with orexin- and melanin-concentrating hormone (MCH)-like immunoreactive neurons in the LH. Our findings strongly suggest that GALP-containing neurons interact with orexin- and/or MCH-containing neurons in the lateral hypothalamus and that it participates in the regulation of feeding behavior in harmony with other feeding-regulating neurons in the hypothalamus.

Effects of galnon, a non-peptide galanin-receptor agonist, on insulin release from rat pancreatic islets

Galanin is a neurotransmitter peptide that suppresses insulin secretion. The present study aimed at investigating how a non-peptide galanin receptor agonist, galnon, affects insulin secretion from isolated pancreatic islets of healthy Wistar and diabetic Goto-Kakizaki (GK) rats. Galnon stimulated insulin release potently in isolated Wistar rat islets; 100 microM of the compound increased the release 8.5 times (p<0.001) at 3.3 mM and 3.7 times (p<0.001) at 16.7 mM glucose. Also in islet perifusions, galnon augmented several-fold both acute and late phases of insulin response to glucose. Furthermore, galnon stimulated insulin release in GK rat islets. These effects were not inhibited by the presence of galanin or the galanin receptor antagonist M35. The stimulatory effects of galnon were partly inhibited by the PKA and PKC inhibitors, H-89 and calphostin C, respectively, at 16.7 but not 3.3 mM glucose. In both Wistar and GK rat islets, insulin release was stimulated by depolarization of 30 mM KCl, and 100 microM galnon further enhanced insulin release 1.5-2 times (p<0.05). Cytosolic calcium levels, determined by fura-2, were increased in parallel with insulin release, and the L-type Ca2+-channel blocker nimodipine suppressed insulin response to glucose and galnon. In conclusion, galnon stimulates insulin release in islets of healthy rats and diabetic GK rats. The mechanism of this stimulatory effect does not involve galanin receptors. Galnon-induced insulin release is not glucose-dependent and appears to involve opening of L-type Ca2+-channels, but the main effect of galnon seems to be exerted at a step distal to these channels, i.e., at B-cell exocytosis.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Galanin- but not galanin-like peptide-containing axon terminals innervate hypophysiotropic TRH-synthesizing neurons in the hypothalamic paraventricular nucleus

Galanin and galanin-like peptide (GALP) are both orexigenic peptides involved in the regulation of food intake and energy metabolism. To determine whether these peptides may directly influence the hypophysiotropic thyrotropin-releasing hormone (TRH)-synthesizing neurons, double-labeling immunocytochemistry was performed at light and electron microscopic levels using antisera against proTRH, galanin and GALP. Galanin-IR axons densely innervated all of the major parvocellular subdivisions of the PVN where proTRH neurons were identified. The periventricular and anterior parvocellular subdivisions exhibited a prominent network of galaninergic nerve fibers, while the density of fibers was less intense in the medial parvocellular subdivision. Galanin-immunoreactive (IR) axon varicosities were juxtaposed to the majority of TRH-synthesizing neurons in the anterior, medial and periventricular subdivisions of the PVN. Ultrastucturally, galanin-IR nerve terminals established symmetric type synapses with the perikarya of proTRH-IR neurons, suggesting an inhibitory nature of these contacts. In contrast, GALP immunoreactive fibers and nerve terminals concentrated primarily in the anterior parvocellular subdivision of the PVN and were found in association with only few proTRH-IR neurons in the periventricular and medial parvocellular subdivisions. In conclusion, the dense innervation of TRH neurons in all subdivisions of the PVN by galanin-IR axons indicates that galanin may be involved in the central regulation of the hypothalamic-pituitary-thyroid axis. In contrast, the relative paucity of GALP-containing axons in juxtapsoition to TRH neurons in the medial and periventricular parvocellular subdivisions of the PVN, the origin of hypophysiotropic TRH neurons, makes it unlikely that GALP similarly exerts direct regulatory effects on hypophysiotropic TRH neurons.

Inhibitory effects of galanin on evoked [Ca2+]i responses in cultured myenteric neurons

Galanin modulates gastrointestinal motility by inhibiting the release of ACh from enteric neurons. It is, however, not known whether galanin also inhibits neuronal cholinergic transmission postsynaptically and whether galanin also reduces the action of other excitatory neurotransmitters. The aim of the present study was thus to investigate the effect of galanin on the evoked intracellular Ca(2+) concentration ([Ca(2+)](i)) responses in myenteric neurons. Cultured myenteric neurons from small intestine of adult guinea pigs were loaded with the Ca(2+) indicator fluo-3 AM, and the [Ca(2+)](i) responses following the application of different stimuli were quantified by confocal microscopy and expressed as a percentage of the response to high-K(+) solution (75 mM). Trains of electrical pulses (2 s, 10 Hz) were applied to stimulate the neuronal fibers before and after a 30-s superfusion with galanin (10(-6) M). Substance P (SP), 5-HT, 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP), and carbachol were used as direct postsynaptic stimuli (10(-5) M, 30 s) and were applied alone or after galanin perfusion. Galanin significantly reduced the responses induced by electrical fiber stimulation (43 +/- 2 to 35 +/- 3%, P = 0.01), SP (15.4 +/- 1 to 8.0 +/- 0.3%, P < 0.01), and 5-HT (26 +/- 2 to 21.4 +/- 1.5%, P < 0.05). On the contrary, galanin did not affect the responses induced by local application of DMPP and carbachol. We conclude that in cultured myenteric neurons, galanin inhibits the excitatory responses induced by electrical stimulation, SP, and 5-HT. Finally, the inhibitory effect of galanin on electrical stimulation, but not on DMPP- and carbachol-induced responses, suggests that, at least for the cholinergic component, galanin acts at the presynaptic level.

Human galanin expresses amphipathic properties that modulate its vasoreactivity in vivo

The purpose of this study was to determine whether human galanin, a pleiotropic 30-amino acid neuropeptide, expresses amphipathic properties in vitro and, if so, whether these properties modulate its vasoactive effects in the intact peripheral microcirculation. We found that human galanin aggregates in an aqueous solution and forms micelles with a critical micellar concentration (CMC) of 0.4 microM. In addition, the peptide interacted with model membrane as indicated by long and significant increase of the surface pressure of the biomimetic monolayer membrane in vitro. Interactions of human galanin with sterically stabilized phospholipid micelles (SMM) were not associated with a significant change in peptide conformation. Using intravital microscopy, we found that suffusion of human galanin alone elicited significant concentration-dependent vasoconstriction in the intact hamster cheek pouch. This response was amplified when human galanin in SSM was suffused onto the cheek pouch. The effects of human galanin alone and in SSM were mediated by galanin receptors because galantide, a galanin receptor antagonist, abrogated galanin-induced vasoconstriction. Collectively, these data show that human galanin expresses amphipathic properties in the presence of phospholipids which in turn amplifies its vasoactive effects in the intact peripheral microcirculation.

Galanin peptide levels in hippocampus and cortex of galanin-overexpressing transgenic mice evaluated for cognitive performance

Galanin-overexpressing transgenic mice (GAL-tg) generated on a dopamine beta-hydroxylase promoter were previously shown to express high levels of galanin mRNA in the locus coeruleus, and to perform poorly on challenging cognitive tasks. The present study employed radioimmunoassay to quantitate the level of galanin peptide overexpression in two brain regions relevant to learning and memory, the hippocampus and cerebral cortex. Approximately 4-fold higher levels of galanin were detected in the hippocampus of GAL-tg as compared to WT. Approximately 10-fold higher levels of galanin were detected in the frontal cortex of GAL-tg as compared to WT. A second cohort of GAL-tg and WT again showed high levels of galanin overexpression in GAL-tg as compared to WT in both brain regions. Correlation analyses were conducted between galanin peptide concentrations and behavioral scores on four learning and memory tasks: the Morris water maze, social transmission of food preference, standard delay fear conditioning, and trace fear conditioning. While some significant correlations were detected, neither hippocampal nor cortical galanin levels in the two cohorts of GAL-tg consistently correlated with performance across these diverse cognitive tasks. Several interpretations of these findings are discussed, including the possibility that a threshold level of galanin overexpression is sufficient to impair performance on learning and memory tasks in mice.

Distribution of galanin receptor 1 immunoreactivity in the rat stomach and small intestine

Galanin affects gastrointestinal functions by activating different G protein-coupled receptors. Here, we identified the sites of expression of the galanin receptor 1 (GAL-R1) subtype in the rat stomach and small intestine by using immunohistochemistry with an antibody raised to the third intracellular loop of rat GAL-R1 (GAL-R1(Y225-238)) and confocal microscopy. Antibody specificity was confirmed by (1) the detection of a band at approximately 70 kDa in Western blot of membranes from GAL-R1 transfected cells, (2) the cell surface staining of GAL-R1 transfected cells, which was not detected in control cells, and (3) the abolition of Western signal and tissue immunostaining by preadsorbing the antibody with the peptide used for immunization. GAL-R1 immunoreactivity was localized to the cell surface of enterochromaffin-like cells, and of myenteric and submucous neurons, and to fibers distributed to the plexuses, interconnecting strands, muscle layers, vasculature, and mucosa. A dense network of GAL-R1 immunoreactivity was observed in the deep muscular plexus in very close association with interstitial cells of Cajal visualized by c-kit immunostaining. In the ileum, 81.6% of GAL-R1 myenteric neurons and 70.7% of GAL-R1 submucosal neurons were substance P immunoreactive. Vasoactive intestinal polypeptide immunoreactivity was found in 48.3% of GAL-R1 submucosal neurons, but not in GAL-R1 myenteric neurons. These findings support the hypothesis that GAL-R1 mediates galanin actions on gastrointestinal motility and secretion by modulating the release of other neurotransmitters and contributes to galanin-induced inhibition of gastric acid secretion by means of the suppression of endogenous histamine release.

Galanin: an endogenous anticonvulsant?

Galanin is a neuroendocrine peptide involved in the regulation of feeding, pain, sexual behavior, learning, and memory. The recent discovery, that galanin antagonized excitatory glutamatergic neurotransmission in the hippocampus, provided a rationale for its possible antiepileptic effects. Here we summarize the data on the effects of galanin on seizure activity in several animal models of epilepsy. Pharmacological and molecular biological evidence suggest potent anticonvulsant effects of galanin. Exogenous administration of galanin receptor agonists attenuated seizures, whereas application of galanin receptor antagonists potentiated seizure expression. Genetically engineered mice, with either deletion or overexpression of galanin gene, showed altered resistance to seizures, which was in direct correlation with galanin gene expression. Possible mechanisms of the anticonvulsant action of galanin include its effects on synaptic potentiation in hippocampal circuits and inhibition of the release of the excitatory neurotransmitter glutamate from principal hippocampal neurons.

Galanin suppresses calcium conductance and activates inwardly rectifying potassium channels in myenteric neurones from guinea-pig small intestine

Whole-cell patch-clamp recording methods were used to investigate the ionic mechanisms underlying the hyperpolarizing action of galanin in enteric neurones. Galanin suppressed calcium current (ICa) and activated inwardly rectifying potassium current (IK,ir) in AH-type myenteric neurones of guinea-pig small intestine. Both suppression of ICa and activation of IK,ir were concentration-dependent, with an EC50 of 1.4 nmol L-1 and 55 nmol L-1, respectively. Pretreatment with pertussis toxin eliminated both actions of galanin, suggesting that both galanin-induced inhibition of ICa and galanin-induced activation of IK,ir involved activation of Gi/Go proteins. Both suppression of ICa and activation of IK,ir by galanin were mimicked by the N-terminal fragment of galanin, galanin-(1-16) suggesting that the first 16 amino acids of the peptide were sufficient for both actions. The galanin receptor antagonist galantide suppressed the galanin-induced activation of IK,ir with an EC50 of 16 nmol L-1. However, galantide alone suppressed ICa. The results suggest two mechanisms of action for galanin: one is opening of inwardly rectifying potassium channels and the second is blockade of voltage-activated calcium channels.

Distribution, regulation and role of hypothalamic galanin systems: renewed interest in a pleiotropic peptide family

1. Galanin peptide and galanin receptor-binding sites are known to be widely distributed within the central nervous system, particularly in the hypothalamus in the preoptic area, the paraventricular (PVN) and supraoptic (SON) nuclei and the arcuate nucleus/median eminence. 2. The present brief review focuses on some recent studies of the regional and cellular localization of mRNA encoding galanin and two galanin receptor subtypes (GalR1 and GalR2) in the hypothalamus, regulation of galanin and/or galanin receptor expression in various nuclei by physiological stimuli, electrophysiological effects of galanin on hypothalamic neurons and the isolation and cloning of galanin-like peptide (GALP), a putative endogenous ligand for GalR2. 3. In situ hybridization studies in rat brain have demonstrated an abundance of GalR1 mRNA in SON, magnocellular (m) and parvocellular (p) PVN and dorsomedial, ventromedial and arcuate nuclei. In contrast, GalR2 mRNA is enriched in pPVN, but not mPVN, and is not detected in SON. In addition, GalR2 mRNA is present in the dorsomedial nucleus and is enriched in the arcuate nucleus compared with GalR1 transcripts, with numerous labelled cells in all subdivisions. 4. Neurons of the SON and PVN contain vasopressin and/or oxytocin, along with several other peptides, and the production and release of these hormones and peptides are modulated by various physiological stimuli. In relation to galanin systems, GalR1 and galanin expression is increased in magnocellular neurons by salt loading and is downregulated by lactation, consistent with an increased inhibition by galanin of vasopressin release following osmotic stimulation and a decreased inhibition of oxytocin release during lactation. 5. Powerful inhibitory effects of galanin on the electrical (and secretory) activity of magnocellular neurons and complex presynaptic actions of galanin on the synaptic release of glutamate in the arcuate nucleus in vitro suggest an active role for multiple galanin receptor subtypes in the regulation of these hypothalamic systems in vivo. 6. The recent isolation of a peptide from porcine hypothalamus (GALP-1-60) that is structurally related to galanin and appears to be selective for GalR2 over GalR1 and the subsequent cloning of GALP cDNA from pig, rat and humans should allow studies to help reveal the physiological role played by galanin receptor subtypes (especially GalR2) and their multiple ligands in the hypothalamus and other brain areas.

Inhibitory neurogenic modulation of histamine-induced cutaneous plasma extravasation in the pigeon

The neurohumoral modulation of the permeability increasing effect of histamine was studied in pigeon skin. Substances were administered through plasmapheresis capillaries inserted into the dorsal wing skin and the protein contents of the perfusates were determined by a quantitative method. The vascular labelling technique was also utilized to histologically identify leaky blood vessels. In the innervated skin histamine evoked a significant, dose-dependent plasma extravasation which was markedly augmented by the coadministration of a specific galanin receptor antagonist, galanin-1-16-bradykinin-2-9-amide (M35). Chronic cutaneous denervation per se resulted in a significant elevation of the permeability-enhancing effect of histamine. In the denervated skin this response was not affected by M35 but was significantly inhibited by galanin. It is concluded that in the normally innervated skin endogenous galanin may exert a neurogenic tonic inhibitory effect on histamine-induced plasma leakage. It is suggested that sensory nerves possess not only pro-inflammatory, but also anti-inflammatory (inhibitory) sensory-efferent functions.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Acute and chronic restraint stress: effects on [125I]-galanin binding in normotensive and hypertensive rat brain

The neuropeptide galanin (GAL) has been implicated in the neural response to a number of stressors including restraint; however, the effect of restraint stress on GAL receptor density in the central nervous system (CNS) has not been investigated. Normotensive (Wistar-Kyoto; WKY) and hypertensive (spontaneously hypertensive; SHR) rats were subjected to a daily 60-min restraint stress paradigm for 0 (control), 1, 3, 5 or 10 consecutive days, and the density of [125I]-GAL binding sites following exposure to restraint was compared between strains using quantitative autoradiography. Significant differences in basal (no stress) levels of GAL receptor density between WKY and SHR were detected in regions such as the central nucleus of the amygdala (Ce) and ventromedial hypothalamus (VMH) (P<0.05). In WKY, restraint stress (1 day) induced significant decreases in GAL receptor density in forebrain regions such as the Ce (-41%) and medial nucleus of the amygdala (-41%) (P<0.05). Chronic restraint (10 days) did not induce significant decreases in these nuclei in WKY, indicating that forebrain neurons containing GAL receptors in WKY possessed a functional ability to adapt to repeated restraint. In addition, restraint stress induced significant decreases in GAL receptor density in SHR in regions such as the lateral parabrachial nucleus (-43%; 5 days of restraint) and hypoglossal nucleus ( approximately -18% for entire restraint period) (P<0.05). In conclusion, restraint stress resulted in region- and strain-specific alterations in GAL receptor density, some of which may contribute to the altered stress response previously observed in hypertensive rats. The results clearly support the hypothesis that neuropeptides such as GAL are an integral component of the neural response to psychological stress, although the functional significance of the changes in GAL receptor density described in this study awaits elucidation.

Multimeric CREB-binding sites in the promoter regions of a family of G-protein-coupled receptors related to the vertebrate galanin and nociceptin/orphanin-FQ receptor families

Four related genes encoding a family of G-protein-coupled receptors (GPCRs) have been isolated from the mollusc Lymnaea stagnalis. The coding regions of this family of receptors share 97-99% sequence similarity at both the protein and nucleotide level, and they also share high sequence identity with vertebrate galanin and orphanin-FQ/nociceptin GPCR families. Analysis of the promoter regions reveals shared domains, some of which encode highly conserved repeating units. One 27-bp repeating unit, which encodes a c-AMP response element (CRE) and binds CREB protein, is repeated 14 times in one promoter. In situ hybridization showed expression of these receptors in identified neurons of several behaviourly important networks including those involved in feeding and ion and water regulation. These Lymnaea receptors are likely to represent members of a novel family of invertebrate neuropeptide receptors extensively regulated in response to intracellular signalling cascades.

Antinociceptive role of galanin in periaqueductal grey of rats with experimentally induced mononeuropathy

The present study was performed in rats with experimentally induced mononeuropathy after left common sciatic nerve ligation. The hindpaw withdrawal latencies to thermal and mechanical stimulation increased significantly after intra-periaqueductal grey injection of 2 or 3nmol, but not 1nmol of galanin in rats with mononeuropathy. Intraperitoneal administration of 4.5mg/kg morphine induced significant increases in hindpaw withdrawal latencies to both noxious stimulation, which were attenuated by following intra-periaqueductal grey injection of 2nmol of the galanin antagonist galantide. Furthermore, the antinociceptive effect induced by intra-periaqueductal grey injection of 26.6nmol of morphine was attenuated significantly by following intra-periaqueductal gray administration of 2nmol of galantide. The results demonstrated that in periaqueductal grey galanin plays an antinociceptive role in rats with mononeuropathy and galanin is involved in the mechanisms of opioid-induced antinociception.

2,3-Dihydro-dithiin and -dithiepine-1,1,4,4-tetroxides: small molecule non-peptide antagonists of the human galanin hGAL-1 receptor

The neuropeptide galanin modulates several physiological functions such as cognition, learning, feeding behavior, and depression, probably via the galanin 1 receptor (GAL-R1). Using an HTS assay based on 125I-human galanin binding to the human galanin-1 receptor (hGAL-R1), we discovered a series of 1,4-dithiin and dithiipine-1,1,4,4-tetroxides that exhibited binding affinity IC50's to hGAL-R1 ranging from 190 to 2700 nM. Two of the dithiepin analogues, 7 and 23, behaved pharmacologically as hGAL-R1 antagonists in secondary assays involving adenylate cyclase activity and GTP binding to G-proteins. Analogues 7 and 23 were also active in functional assays involving galanin, reversing the inhibitory effect of galanin on acetylcholine (ACh) release in rat brain hippocampal slices and electrically-stimulated guinea pig ileum twitch.

Galanin receptor subtypes

The neuropeptide galanin, which is widely expressed in brain and peripheral tissues, exerts a broad range of physiological effects. Pharmacological studies using peptide analogues have led to speculation about multiple galanin receptor subtypes. Since 1994, a total of three G-protein-coupled receptor (GPCR) subtypes for galanin have been cloned (GAL1, gal2 and gal3). Potent, selective antagonists are yet to be found for any of the cloned receptors. Major challenges in this field include linking the receptor clones with each of the known physiological actions of galanin and evaluating the evidence for additional galanin receptor subtypes.